# Contingency tables ¶

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A contingency table (tableau de contingenc/à double entrées) is a table of the unique values of a vector by the number of times this value is present.

# picking 50 values within [0,10]
vect <- sample(0:10, 50, replace = TRUE)
table(vect)
# 0  1  2  3  4  5  6  7  8  9 10
# 4  6  4  6  5  5  5  6  6  1  2


You can read that each of your eleven values was at least picked once. For instance, we picked $10$ twice.

## Frequencies table ¶

You can use prop.table to get the frequency of each value instead of the number of occurrences.

• prop.table(table(v), 1) (line only)
• prop.table(table(v), 2) (column only)

## More complex tables ¶

If you are calling a table like the code above, so while providing a qualitative variable (the unique values), and a quantitative variable (the values)

table(ech$qual, ech$quant)


Then you may try to use

xtabs(~ qual + quant, ech)


The main difference is that xtabs is using formulas, so when you learned them, you will be able to do quite the great contingency tables.